Vehicles have been developed to perform an idle-stop when idle-stop conditions are met and automatically restart the engine when restart conditions are met. Such idle-stop systems enable fuel savings, reduction in exhaust emissions, reduction in noise, and the like.
Engines may be restarted from the idle-stop condition automatically, without receiving an operator input, for example, in response to engine operating parameters falling outside a desired operating range. Alternatively, engines may be restarted from the idle-stop condition in response to a vehicle restart and/or launch request from the operator.
However, the inventors have recognized several potential issues with such a system. As one example, if a driver has a change of mind while the engine is being shut down (e.g., still spinning down) and wishes to immediately restart the engine, a desirable fast restart may not be possible. Specifically, the driver may have to wait for the engine to stop rotating completely before the engine starter can be re-engaged. As such, this may substantially increase the change of mind restart time and thus degrade the quality of the restart operation.
Thus in one example, the above issue may be addressed by a method of controlling a vehicle system including an engine that is selectively deactivated during engine idle conditions, the method comprising, adjusting a brake torque applied to a deactivated rotating engine after an engine restart request, the brake torque applied to slow the engine to at least a predetermined threshold speed without stopping the engine, and engaging a starter to the still rotating engine to increase the engine speed and restart the engine.
In one example, during the execution of an engine idle-stop operation, a driver may change their mind and request an immediate restart (e.g., by releasing a brake pedal). In response, a controller may be configured to restart the engine via a starter motor with the engine still spinning, that is, without necessitating a complete engine stop. As such, an engine starter may be configured to be engaged at engine speeds above zero, for example, at or below a predetermined threshold speed (such as at or below 50 rpm, or at or below 100 rpm). If the engine speed at the time of restart request is at or below the predetermined threshold, the starter may be immediately engaged to the still rotating engine to increase engine speed and enable an immediate restart. Alternatively, if the engine speed at the time of restart request is above the predetermined threshold, the controller may adjust a brake torque that is applied to the engine to more rapidly and forcefully slow the engine to at least the predetermined threshold starter engagement speed. Once the threshold speed is attained, the starter may be engaged to the still rotating engine to increase engine speed and restart the engine. The brake torque employed may include one or more of a reverse torque (for example, by clutching in the alternator or the AC compressor), an output shaft torque or a transmission drag torque (for example, by clutching in the transmission), a gas torque (for example, by deactivating the cylinders), or a combination thereof. By expediting engine slow-down to the starter threshold speed and engaging the starter to the still rotating engine, a rapid restart and vehicle launch may be achieved without requiring prior complete engine shut-down. However, it will be appreciated that if a prior engine full stop is desired (for example, as determined by the driver, or by the engine controller), a restart may alternatively be performed only after fully stopping the engine, but again optionally using a brake torque to rapidly slow the engine to rest.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.